The composite coupling devices described and claimed in my aforementioned applications comprise a "driver", or heat-recoverable member, made from a memory metal and a second, sleeve member, usually an insert member, which is so constructed, and/or fabricated from such a material, that it enhances the coupling of the composite device to a substrate or substrates. Typically, the "driver" member and the "insert" member are both generally tubular and the insert member is provided with teeth and/or is made from a gall-prone material and/or is provided with portions, such as slots or grooves, of relative weakness, and/or is made from a material with desirable properties, e.g. electrical properties, having regard to the particular application of the composite coupling device.
As is explained in the above applications, "memory metals" are alloys which exhibit changes in strength and configurational characteristics on passing through a transition temperature, in most cases the transition temperature between the martensitic and austenitic states, and can be used to make heat-recoverable articles by deforming an article made from them whilst the metal is in its martensitic, low temperature, state. The article will retain its deformed configuration until it is warmed above the transition temperature to the austenitic state when it will recover towards its original configuration. The deformation used to place the material in the heat-unstable configuration is commonly referred to as thermally recoverable plastic deformation and can also, in certain cases, be imparted by introducing strains into the article above the transition temperature, whereupon the article assumes the deformed configuration on cooling through the transition temperature. It should be understood that the transition temperature may be a temperature range and that, as hysteresis usually occurs, the precise temperature at which transition occurs may depend on whether the temperature is rising or falling. Furthermore, the transition temperature is a function of other parameters, including the stress applied to the material, the temperature rising with increasing stress.
Amongst such memory metals there may especially be mentioned various alloys of titanium and nickel which are described, for example, in U.S. Pat. Nos. 3,174,851, 3,351,463, 3,753,700, 3,759,552, British Patent Nos. 1,327,441 and 1,327,442 and NASA Publication SP 5110, "55-Nitinol-The Alloy with a Memory, etc." (U.S. Government Printing Office, Washington, D.C. 1972), the disclosures of which are incorporated herein by reference. The property of heat recoverability has not, however, been solely confined to such titanium-nickel alloys. Thus, for example, various copper-based alloys have been demonstrated to exhibit this property in, e.g. N. Nakanishi et al, Scripta Metallurgica 5, 433-440 (Pergamon Press 1971) and such materials may be doped to lower their transition temperatures to cryogenic regimes by known techniques. Similarly, type 304 stainless steels have been shown to enjoy such characteristics, E. Enami et al, id at pp. 663-68. These disclosures are similarly incorporated herein by reference.
In general, the alloys are chosen to have transition temperatures between the boiling point of liquid nitrogen, -196.degree. C., and room temperature as the lowest temperature likely to be encountered in operation, i.e. between -196.degree. C. and -75.degree. C. in many aerospace applications. This enables the articles made from the alloys to be deformed to the configuration from which recovery is desired, and stored, in liquid nitrogen and yet insures that after heat recovery there is no danger of loss of mechanical strength during use by reason of the article encountering a temperature at which it reverts to the martensitic state.
However, storage of the deformed article in liquid nitrogen is inconvenient. Recently processes have been developed by which metallic compositions, particularly certain copper-based alloys, can have the transition temperature at which they revert to the austenitic state transiently elevated from the normal temperature at which this occurs to a higher temperature, typically above room temperature. Subsequent recovery requires that the article be heated. Such alloys are referred to as being "preconditioned". Procedures by which they are preconditioned are described in U.S. applications by G. B. Brook et al filed Feb. 19, 1975 entitled "Heat Treating Method", Ser. No. 550,847; and now abandoned "Mechanical Preconditioning Method", Ser. No. 550,555; now U.S. Pat. No. 4,036,669 issued July 19, 1977; and "Austenitic Aging of Metallic Compositions", Ser. No. 550,556, now U.S. Pat. No. 4,067,752 issued Jan. 10, 1978, the disclosures of which are incorporated by reference.
As indicated above, by application of a preconditioning process to an alloy its transition temperature can be elevated. However, once recovery has been brought about by heating the article through its new transition temperature, the alloy's response to temperature change reverts to that it possessed prior to preconditioning. Accordingly, it remains austenitic until cooled to the temperature at which transition to martensite normally occurs, typically chosen to be at 0.degree. C. or below depending upon the temperature environment likely to be encountered.
A typical application for the composite couplings described in the aforementioned Martin applications is to join tubular or cylindrical substrates. Properly dimensioned, these couplings can be employed to join substrate that vary greatly in size. For example, they might find application in joining tubing sections that could be used for hydraulic systems in aircraft. They can also be used to join sections of pipe of very large dimension.
In many situations the tolerance criteria for the cylindrical substrate to be joined are such that there can be significant variation in size between sections, for example on the order of 5% or even more, and the substrate may be significantly out of round. Also, it is frequently desired to connect substrates that vary somewhat in size. Accordingly, there is a need for composite couplings capable of accommodating such irregularities or variations in the substrate. The principal object of this invention is to provide such devices.